Broadband Network
Architectures
Router Design
TEMangir Sp02
Routing1
Outline






Introduction
Router Fundamentals
Routing Algorithms and Protocols
Fast Forwarding
Layer-3 Switching
IP over WDM
TEM 497
Routing2
Introduction
Routing3
A Fine Distinction
 Imprecision surrounds the terms “routing” and
“forwarding”
 Forwarding is the act of transferring a packet
from one interface of a router to another, after
consulting a forwarding table
 Routing is the act building routing tables by
means of a routing algorithm
 We frequently abuse this convention
TEM 497
Routing4
What is a Router?
 A packet forwarder
 Multiprotocol – IP, IPX, AppleTalk
 A routing-protocol execution machine
 Multiprotocol – IGRP, RIP, OSPF, IS-IS




A
A
A
A
TEM 497
packet monitor
general-purpose computer
firewall
switch
Routing5
Internet Forwarder
Functions








Parse the datagram header
Checksum actions
Select the network protocol
Decrement the TTL field
Use the TOS field to prioritize the datagram
Process the options fields
Forward (route) the datagram to next hop
Fragment the datagram
TEM 497
Routing6
Internet Router Functions
 Execute one or more routing protocols
 Exchange state information with other routers
 Use a transport protocol
 Authentication
 Collect network-management statistics
 Packet counts, lengths, and types
 Source-destination matrix
 Configuration support
 User interface
 Tunnel management
TEM 497
Routing7
Internet Firewall Functions
 Filtering of destinations
 Source
 Destination
 Filtering of services
 Block protocols
 Block transport port numbers
 Virtual private networks
FTP
HTTP
X
Port
Nums
UDP
TCP
Proto
ID
IP
 Encrypted tunnels
TEM 497
Routing8
Control and Data Planes
Control Plane
control packets to &
from other control
plane entities
data packets to &
from other data
plane entities
Route
Determination
Function
Data
Forwarding
Function
control packets to &
from other control
plane entities
data packets to &
from other data
plane entities
Data Plane
Router
TEM 497
Routing9
Router Fundamentals
Routing10
ARP
 Address Resolution Protocol translates an
IP address to a media (link) address
 Simple request-response protocol
 First host broadcasts a request packet
containing desired IP address
 Second host recognizes its IP address
 Second host sends a response packet to first
host containing its media (link) address
 First host caches address mapping for later use
TEM 497
Routing11
ARP Header
0
15
Hardware Type
HLen
PLen
31
Protocol Type
Operation
Source Hardware Address
Source Protocol Address
Target Hardware Address
Target Protocol Address
TEM 497
Routing12
ARP Header Fields
 Hardware type: e.g. Ethernet = 1
 Protocol type: e.g. IPv4 = 0080
 HLen: Hardware address length (e.g. Ethernet =
48 bits)
 PLen: Protocol address length (e.g. IPv4 = 32
bits)
 Operation: a query (0) or a reply (1)
 Source: where packet came from
 Target: system it is querying about
TEM 497
Routing13
ARP Operation (1)
DNS
FTP
FTP
(8)
TCP
TCP
(8)
(1)
(2)
IP
(8)
ARP
(7)
Ethernet
Driver
ARP
(3)
IP
(8)
Ethernet
Driver
ARP
(6)
(5)
Ethernet
Driver
(4)
TEM 497
Routing14
ARP Operation (2)
1. IP datagram with destination address
2. Next-hop address is passed to ARP
3. ARP request passed to Ethernet driver
4. ARP request broadcast in Ethernet frame
Routing ARP request recognized by next-hop node
6. ARP reply sent by next-hop node
7. ARP reply updates ARP cache
8. IP datagram sent through next-hop node
TEM 497
Routing15
Proxy ARP
 Allows a router to answer ARP requests
from one of its networks for a host on
another of its networks
 Router substitutes its link address for the
responding host’s
 Proxy gives the illusion that the host is
connected to another network
TEM 497
Routing16
RARP
 Reverse ARP translates a media (link)
address to an IP address
 Used by system without nonvolatile
storage
 Requires a network-wide RARP server
 Similar to BOOTP (Bootstrap Protocol)
TEM 497
Routing17
Router Advertisement (1)
 Routers announce presence by
broadcasting ICMP router advertisements
 All-hosts multicast address: 224.0.0.1
 Limited broadcast address: Routing
Advertisements are periodic
 7-minute period
 Advertisement becomes stale after 30 minutes
TEM 497
Routing18
Router Advertisement (2)
 Advertisements contain a list of addresses
 Router IP addresses
 Preference level of each address
 Higher values are preferred
 Highest value is the normal router
 Lower value is a backup router
 Lowest values do not wish to receive default traffic
TEM 497
Routing19
Router Solicitation (1)
 A host should not have to wait 7 minutes for the
next ICMP router advertisement
 ICMP router solicitation messages allow the host
to request the identity of a router
 The host broadcasts the solicitation
 All-routers multicast address: 224.0.0.2
 Limited broadcast address: 255.255.255.255
 The host receives many advertisements
 The host chooses the router on its subnet
TEM 497
Routing20
Router Solicitation (2)
 Host bootstrap operation
 Broadcasts 3 solicitations
 Broadcasts 1 message every 3 seconds
 Broadcasting stops as soon as a valid router
advertisement is received
TEM 497
Routing21
Broadcast Storms
 Mechanisms that rely on broadcasting messages
within a LAN are vulnerable to broadcast
storms, i.e. long, uncontrolled exchanges of
broadcast packets.
 Because everyone must process a broadcast,
storms put a heavy load on uninvolved nodes.
 Therefore, protocol exchanges – such as ARP,
RARP, DHCP, Router Solicitation, and Router
Announcement – must control broadcasts with
timers and by limiting message counts.
TEM 497
Routing22
Redirect
 ICMP redirect error is sent by a router to a
host to indicate that the host should send
its datagrams through another router
1. First Datagram
4. Successive Datagrams
2. Redirect
3. First Datagram
Security concern!
TEM 497
Routing23
A Simple Router
I/O Bus
CPU
DMA
Ctrl
3
2
System
Bus
1
DMA
Xfer
Main
Memory
1. Packet input
2. Header processing
Routing table lookup
DMA transaction
TEM 497
3. Packet output
NIC
Fast Ethernet
NIC
FDDI
NIC
ATM
NIC = Network Interface Controller
DMA = Direct Memory Access
Routing24
IP-Layer Processing
Routing
Algorithm
Routing
Table Mgmt
UDP
TCP
Yes
ICMP
Data
Control
Routing
Table
IP Output
Calculate
Next Hop
IP Layer
TEM 497
Network Output(s)
No
Addressed
Here?
Forwarded
Packet
Source
Routed
Packet
Process
IP Options
IP Input
Queue
Network Input(s)
Routing25
Routing Table Structure
 Destination IPv4 address
 Host address (32 bits)
 Network address (<32 bits)
 Next-hop router IP address
 Router on a directly connected network
 Flags
 Network or host
 Router or interface
 Network interface
TEM 497
Routing26
Routing Table
Host address
Multicast address
zap % netstat -rn
Routing tables
Destination
128.9.192.24
128.9.192.72
128.9.192.73
224.0.0.9
127.0.0.1
128.9.192.146
128.9.192.100
128.9.192.69
128.9.192.126
default
128.9.192.0
128.9.112.0
Loopback address
Next-hop router
Gateway
128.9.112.24
128.9.112.72
128.9.112.73
127.0.0.1
127.0.0.1
128.9.112.146
128.9.112.100
128.9.112.69
128.9.112.126
128.9.112.72
128.9.192.151
128.9.112.151
Network address
TEM 497
Flags
UGH
UGH
UGH
UH
UH
UGH
UGH
UGH
UGH
UG
U
U
U = route
G = route
H = route
D = route
Refcnt
0
9
0
1
8
0
0
0
0
22
7
0
is up
is via gateway
is to a host
was redirected
Use
0
54173
0
118606
3541986
0
0
0
0
8601210
2109258
51
Interface
myri0
myri0
myri0
lo0
lo0
myri0
myri0
myri0
myri0
myri0
le0
myri0
Ethernet
Loopback
Myrinet
Routing27
IP Output Processing
 Search table for match of host address
 If found, then send datagram to next-hop router or
directly connected interface
 Search table for match of network address
 If found, then send datagram to next-hop router or
directly connected interface
 Use subnet mask, if necessary
 Search table for default entry
 If found, then send the datagram to next-hop router
TEM 497
Routing28
Routing
 Assumptions
 Router knows the addresses of all other routers
 Router knows the “costs” to reach its neighbors
 Network viewed as a collection of nodes and
(bidirectional) links
 From any given router find next hop on shortest
path to any other router
 Tolerance of failures
TEM 497
Routing29
Distance-Vector Routing
 Based on the sharing of distance vectors
 A router’s distance vector is a list of its “distances” to
every other router in the routing domain
 Router tells its neighbors its distance (cost) to
every other router in the network
 Cost = Distance
 Usually we assume that cost = distance = hops
 Other metrics: bandwidth, delay, charging
TEM 497
Routing30
Distance-Vector Algorithm
 Router maintains a distance vector
 List of <dest, cost> entries
 Router periodically sends a copy of its distance
vector to all neighboring routers
 Upon receipt of a distance vector, the router
determines its new distance vector
 cost(v)  min {cost(v), costw(v)+cost(w)}
 Converges to shortest-path routes
 O(MN), M=num_links, N=num_nodes
TEM 497
Routing31
Distance-Vector Problems
 Slow convergence
 Packet bouncing after link failure
 Counting to infinity
 Race condition after network partition
 Algorithm keeps adding to current cost, never
reaching infinity
 Solution: represent infinity by a large number
 Large number is 16 in RIP
 Caused by routers repeating information that
was valid before failures
TEM 497
Routing32
Link-State Routing
 Based on sharing of link state
 Link-state packets: <ID, Nbr_ID, cost>
 Link-state information is flooded throughout the
network
 Each router computes shortest paths
independently
 Router tells every other router its distance (cost)
to its neighbors
 Cost = distance = hops
TEM 497
Routing33
Link-State Algorithm
 Router maintains a database of link-state
packets that describe its links
 Router floods a copy of every link-state packet
throughout the network
 Uses sequence numbers and duplicate elimination to
control the flood
 Router applies Dijkstra algorithm to find shortest
path
 Converges to shortest-path routes
 O(M logM), M = num_links
TEM 497
Routing34
LS
LS
LS
Router
All Other
Routers
LS
Router’s
Neighbors
DV
Router
DV
DV
Two Routing Schemes
Distance Vector Routing
Link State Routing
Router sends a large amount of
information to a few recipients
Router sends a small amount of
information to many recipients
TEM 497
Routing35
Link-State & DistanceVector Routing
 Link-state
 Loopless routing
 Fast convergence
 Precise, multiple metrics (costs)
 Distance-vector
 Simplicity
 Less memory required
 Both in use in today’s Internet
TEM 497
Routing36
Internet Routing Hierarchy
 Interior routing
 Within an AS
 Intradomain routing
 Exterior routing
 Between ASs
 Interdomain routing
TEM 497
Routing37
Internet Routing Protocols
 Interior Gateway Protocols (IGPs)






RIP
RIPv2 is the current standard
IGRP
EIGRP
OSPF
IS-IS
 Exterior Gateway Protocol (EGP)
 Border Gateway Protocol (BGP)
 BGP-4 is the current standard
TEM 497
Routing38
Routing Protocol
Comparison
Routing
Protocol
Supported
Protocols
Strengths
Enhanced IGRP
IP, IPX,
AppleTalk
load balancing,
metrics
IGRP
IP, OSI-IP
RIPv2
IP
simplicity
improved
convergence
OSPF
IP
rapid
convergence
complexity
IS-IS
IP, OSI-IP
RIP
IP
simplicity
count to 
TEM 497
Limitations
Routing39
IGP Example
128.9.1.2
Rtr A
Rtr B
s1
e0
128.9.2.0/24 (2000)
s2 128.9.3.0/24 (60)
.2
128.9.Routing2
.2
128.9.4.0/24 (60)
Rtr C
128.9.1.0/24 (10)
128.9.Routing0/24 (10)
128.9.6.0/24 (10)
RIP Routing Table at Rtr A
Destination
129.9.1.0
128.9.2.0
128.9.3.0
Next Hop
e0
s1
s2
128.9.2.2 (s1)
128.9.4.0
128.9.3.2 (s2)
128.9.Routing0128.9.2.2 (s1)
128.9.6.0 128.9.3.2 (s2)
TEM 497
Hop Count
1
1
1
1
OSPF Routing Table at Rtr A
128.9.6.2
Destination
129.9.1.0
128.9.2.0
128.9.3.0
Next Hop
e0
s1
s2
Hop Count
-
128.9.4.0
128.9.3.2 (s2)
120
128.9.Routing0128.9.2.2 (s1)
128.9.6.0 128.9.3.2 (s2)
130
70
Routing40
Lollipop Sequence Space
Problem: Sequence numbers of link-state packets wrap around or are restarted
a
-N/2
0
d
N/2 - 1
Sequence numbers
start here (bootup)
and circle around
repeatedly
TEM 497
b
If d<N/4 (half
circumference) then
b is the newer
sequence number,
otherwise a is
newer
Sequence numbers in this subspace are generated
only after bootup, and recipients notify the
booting router of last sequence number received
Routing41
Routing in the Internet
 Autonomous System (AS)
 Set of routers and hosts administered by a
single entity
 Customer network (e.g., 128.9.0.0)
 ISP
 Backbone provider
 Assigned a unique 16-bit number
 AS represents a routing domain
TEM 497
Routing42
Classification of ASs (1)
 Stub AS
 Single connection to another AS
 All traffic is local (i.e., originates or terminates at the
AS)
 E.g., a typical corporation
 Multihomed AS
 Multiple connections to other ASs
 Refuses to carry nonlocal (transit) traffic
 E.g., a well-connected corporation
TEM 497
Routing43
Classification of ASs (2)
 Transit AS
 Multiple connections to other ASs
 Accepts local and nonlocal (transit) traffic
 E.g., ISP or backbone operator
TEM 497
Routing44
Types of ASs
AS 4
(stub)
AS 2
(transit)
AS 1
(transit)
AS 5
(stub)
AS 6
(multihomed)
TEM 497
AS 3
(transit)
Routing45
First 20 AS Numbers
AS Number
Name
Handle
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
GNTY-1
DCN-AS
MIT-GATEWAYS
ISI-AS
SYMBOLICS
BULL-HN
UK-MOD
RICE-AS
CMU-ROUTER
CSNET-EXT-AS
HARVARD
NYU-DOMAIN
BRL-AS
COLUMBIA-GW
NET-DYNAMICS-EXP
LBL
PURDUE
UTEXAS
CSS-DOMAIN
UR
[CS15-ARIN]
[DW19-ARIN]
[RH164-ARIN]
[JKR1-ARIN]
[SG52-ARIN]
[JLM23-ARIN]
[RNM1-ARIN]
[RUH-ORG-ARIN]
[HC-ORG-ARIN]
[CS15-ARIN]
[WJO3-ARIN]
[ZN68-ARIN]
[RR33-ARIN]
[ZC26-ARIN]
[ZSU-ARIN]
[CAL3-ARIN]
[JRS8-ARIN]
[DLN12-ARIN]
[CR11-ARIN]
[LB16-ARIN]
http://www.arin.net/library/internet_info/asn.txt
TEM 497
Routing46
CIDR — Problems
 Classless Interdomain Routing (CIDR)
 Class A IP addresses are too large (16M hosts)
 Class C IP addresses are too small (256 hosts)
 Class B addresses are just right (64K hosts), but we
are running out of class B addresses
 Routing table explosion
 Core routers act upon network numbers
 Routing tables grow as number of networks increases
TEM 497
Routing47
CIDR — Solutions
 Allocate the class C address space among
geographical regions
 Europe, the Americas, Asia, Africa
 Eases routing problems
 Assign blocks of class C addresses to
users
 Can attach more than 256 hosts
 Allows for the aggregation of routes
TEM 497
Routing48
CIDR — Rules
 User may ask for 2n contiguous class C
address blocks (0  n  5)
 Yields 2n+8 host addresses
 A block of class C addresses is listed in a
core routing table by address prefix
 Like a subnet mask
 E.g., the prefix 192.4.16.0/20 specifies
network numbers 192.4.16.0 through
192.4.31.255
TEM 497
Routing49
CIDR Aggregation
Routing Table
192.4.16.0/20
One routing
prefix replaces
4096 entries
4096 Customer Addresses
192.4.16.0 - 192.4.31.255
Customer
Backbone Provider
ISP
“192.4.16.0/20” is shorthand notation for “192.4.16.0 - 192.4.31.255”
TEM 497
Routing50
CIDR Block Allocations
194.0.0.0
198.0.0.0
200.0.0.0
202.0.0.0
fewer
fewer
fewer
fewer
fewer
fewer
fewer
TEM 497
– 195.255.255.255: Europe
- 199.255.255.255: North America
- 201. 255.255.255 : Central and South America
- 203. 255.255.255 : Asia and the Pacific
than
than
than
than
than
than
than
256 addresses:
512 addresses:
1024 addresses:
2048 addresses:
4096 addresses:
8192 addresses:
16384 addresses:
1 class C network
2 class C networks
4 class C networks
8 class C networks
16 class C networks
32 class C networks
64 class C networks
Routing51
Network Address
Translation
 A form of IP masquerading
 Used when a large customer network can obtain
only a small IP address allocation
 For example, a corporation with thousands of
hosts receives only a class C address space
 Private network address space used internally
 10.0.0.0/8
 172.16.0.0/12
 192.168.0.0/16
TEM 497
Routing52
User Tools for Routing
 netstat
 Unix and MS-DOS
 Display routing table with -rn
 arp
 Unix and MS-DOS
 Examine or modify the ARP cache
 ifconfig
 Unix
 Report details of network interfaces with -a
TEM 497
Routing53
Evolution of Router Design
 Generation 1: shared backplane and
shared buffer memory
 Generation 2: shared backplane and local
buffer memory
 Generation 3: switched backplane and
local buffer memory
 Generation 4: clusters of routers
TEM 497
Routing54
Generation 1
PACKET
BUFFERS
CPU
BACKPLANE
BUS
LINK
INTERFACE
CARDS
TEM 497
DMA
DMA
DMA
MAC
MAC
MAC
Routing55
Generation 2
CPU
BACKPLANE
BUS
DMA
LINK
INTERFACE
CARDS
PACKET
BUFFERS
MAC
TEM 497
DMA
DMA
PACKET
BUFFERS
PACKET
BUFFERS
MAC
MAC
Routing56
Generation 3
CPU
SWITCH
DMA
LINK
INTERFACE
CARDS
PACKET
BUFFERS
MAC
TEM 497
DMA
DMA
PACKET
BUFFERS
PACKET
BUFFERS
MAC
MAC
Routing57
Generation 4
LINK
INTERFACES
R
O
U
T
E
R
R
O
U
T
E
R
R
O
U
T
E
R
FAST INTERCONNECT
TEM 497
Routing58
Fast Forwarding
Routing59
Cisco Forwarding
Performance
Switching
Path
Cisco 2500
Cisco 4500
Cisco 7000
Cisco 7500
Process
1000 pps 10,000 pps
2500 pps
10,000 pps
Fast
6000 pps 45,000 pps
30000 pps
150,000 pps
271,000 pps
275,000 pps
Hardware
TEM 497
N/A
N/A
Routing60
Cisco Performance Notes
 Process
 Fast
 Hardware
TEM 497
Routing61
Importance of Lookups
 The routing table must have an entry for every
possible Internet address
 Routing-table size has grown steadily
 The problem is to match the destination address
of an incoming packet to a routing-table entry in
a small amount of time
 Entry is usually an aggregated prefix
 Best (longest) prefix match
TEM 497
Routing62
Routing Table Growth
TEM 497
www.telstra.net/ops/bgptable.html
Routing63
Address Lookup
 Router must be able to look up all assigned IPv4
addresses
 Millions of addresses are assigned
 There is not enough high-speed memory to
store all assigned IPv4 (and IPv6) addresses
 We must aggregate addresses to compress the
routing table as much as possible
TEM 497
Routing64
Address Aggregation
Address
Interface
Address
Interface
128.9.160.38
8
128.9.0.0/16
8
128.9.191.7
8
128.0.0.0/1
4
154.23.16.134
4
128.0.0.0/6
1
194.47.10.72
4
171.9.0.0/16
5
128.12Routing50.89 1
193.0.0.0/4
3
130.39.213.66
1
193.9.14.0/24
5
171.9.160.38
5
193.77.50.7
3
193.9.14.38
5
202.197.160.67
3
Compressed Table
Original Table
TEM 497
Routing65
A Simple Scheme
 In IPv4 at most only the first 24 bits are used by
core routers
 Those bits specify the network number toward which
the packet is headed
 Given a fast random-access memory of 224
locations (16 Mword), we can store the next hop
of net address x.y.z.* in memory location x.y.z
 Only one memory access per lookup is needed
TEM 497
Routing66
Updating Routing Tables
 Compressed routing tables must be
updated periodically
 New information about routes can affect
address aggregation
 The compression effort can be significant
 Compression must be computationally
efficient
TEM 497
Routing67
Hash Tables for Fast
Address Lookup
Length
8
TEM 497
Hash
Lists of Prefixes
10
12
10.128, 10.64
16
10.1, 10.2
24
10.1.1, 10.1.2, 10.2.1
Routing68
Level-1 Lookup Scheme
IP Address
31
10
2 4
0
16
0
bix
bit
1
15
0
ix
code[4K]
six ten
675
base[1K]
maptable[676]
pointer = +
TEM 497
+
Routing69
Level-2/3 Lookup
 Level-1 pointer points to either:
 Next hop, or
 Indicator to continue search at levels 2/3
 Levels 2/3 use the lower 16 bits of the
address to look up the next hop
TEM 497
Routing70
Performance of Scheme
 Data structures fit in data cache memory
 Fewer than 100 instructions per address
are required for lookup
 Therefore, can forward several million
packets per second through a
conventional CPU-based router
TEM 497
Routing71
Layer-3 Switching
Routing72
Tag Switching
 Sometimes called layer-3 or IP switching
 Combines a switch with a router
 Fast switch
 Slower router
 Attempts to detour around the slow
routing path by taking a fast switching
path
TEM 497
Routing73
Observations (ca. 1997)
 Routers are expensive and slow
 $187,000 for 1-Gb/s router
 Switches are cheap and fast
 $41,000 for 5-Gb/s switch
 It costs 20 times as much to route a bit as
to switch it
TEM 497
Routing74
IP Flows
 A flow is a stream of IP packets that follow the
same route for several hops
 Common flow types
 Streams from a specific source address to a specific
destination address
 Streams from a specific source address/port to a
specific destination address/port
 Flows have limited lifetimes
 Analogous to a VC
TEM 497
Routing75
Flow Classification
 Flows should be long-lived
 Disregard DNS packets
 Disregard ICMP packets (e.g., ping)
 Disregard most HTTP packets
 Flows should be high-throughput
 Disregard Telnet sessions
 Detect a flow if the number of packets received
in a specified time interval exceeds a threshold
TEM 497
Routing76
Flow Statistics
 Count packets and flows over a period of
time
 Flow is defined by IP source and destination
addresses
 Measure the duration of each flow
 Count the number of packets in each flow
TEM 497
Routing77
Flow Statistics Illustrated
100
PERCENTAGE
FLOWS
50
PACKETS
0
0
50
100
150
200
250
300
FLOW DURATION (seconds)
TEM 497
Routing78
Flows and Packet Traces
Protocol
News
(NNTP+TCP)
Mbone
(IP in IP)
X Windows
(TCP)
FTP Data
(TCP)
Rlogin
(Telnet+TCP)
Web
(HTTP+TCP)
Mail
(POP+TCP)
Mail
(SMTP+TCP)
Management
(SNMP+TCP)
Name Server
(DNS+UDP)
TEM 497
Packets/s
Flows/s
Flow Duration (s) Packets/Flow
1096
0.7
177
627
456
0.1
173
2307
111
0.2
161
276
2018
2.2
118
525
803
4.2
114
114
6717
73.0
57
74
9
0.4
27
21
802
49.5
18
15
43
6.1
18
6
929
216.6
15
4
Routing79
Flow Classifier
 X/Y flow classifier
 Flow recognition by stream characteristics
  X packets
  Y seconds
 Flow is declared switchable
 Flow deletion by stream characteristics
  W packets
  Z seconds
 Flow is declared unswitchable
 Analogous to calculating first derivative df/dt
TEM 497
Routing80
Basic Tag-Switch Strategy
 Determine whether a flow exists
 Use normal hop-by-hop IP forwarding for
short-lived flows
 Use “short-cut” ATM switching for longlived, high-throughput flows
TEM 497
Routing81
Tag-Switch Architecture
Remove from ATM switch
Signaling
LANE
MPOA
IS-IS routing
IP Switch
Controller
Add to ATM switch
Flow management protocol
Switch management protocol
Flow classifier
ATM
Switch
Claim: added software is 10% the size of removed software!
TEM 497
Routing82
Default Mode
Controller
IP flow is initially
forwarded
Two default VCs
are used
Downstream
Upstream
Switch
TEM 497
Routing83
Flows Detected
Controller detects a
flow
Instructs upstream
switch to use a new VC
Upstream flow is now
labelled by a new VC
Controller
Downstream controller
detects a flow
Instructs this switch to
use a new VC
Downstream flow is
now labelled by a new VC
Downstream
Upstream
Switch
TEM 497
Routing84
Cut-Through Action
Controller directs the
switch to reconfigure
Two VCs are joined into
one VC
Flow is now carried at
switching speeds
Periodic messages to
maintain new VC
Timeout of inactive
flows
Controller
Downstream
Upstream
Switch
TEM 497
Routing85
Features of Tag Switching
 IP header and LLC/SNAP encapsulation header
can be removed
 Compression benefits throughput
 Added back later at the exit tag switch
 TTL is adjusted at the exit tag switch
 Preserve the value that it would have had in default
mode
 Update the IP checksum too
 Avoids mismatches in TTL for a flow
TEM 497
Routing86
Tag-Switching Performance
 Analysis based on San Francisco NAP packet
traces
 Evaluate switching gain, i.e. the fraction of all
packets that are directly switched
 Simulations of Ipsilon IP switch
 86% of packets are switched
 92% of bytes are switched
 Switching gain is maximized at a detection threshold
of about 10 packets
TEM 497
Routing87
Layer-3 Switching
 Data-driven approaches: use only packet
statistics
 Ipsilon IP Switching
 Cisco Tag Switching
 Topology-driven approaches: use routingtable or other topological information
 IBM ARIS
 Multiprotocol Label Switching (MPLS)
TEM 497
Routing88
MPLS
 Multiprotocol Label Switching (MPLS)
 Generalized MPLS (GMPLS)
TEM 497
Routing89
IP over WDM
 Place IP flows on their own lightpaths
 Lightpath is formed by the concatenation of
wavelengths
 Lightpath is all-optical
 Idea is similar to IP switching
 Wavelength-selective crossconnect (vs. ATM cell
switch)
 There are only a few wavlelengths to carry flows (vs.
many ATM virtual channels)
 A signaling protocol is required to set up
lightpaths
TEM 497
Routing90