Novel Networks
Theo Benson
• Cellular Networks
• Data Center Networks
• Current Class Grades
Mobile Traffic: Path Features
Mobile
Network
Internet
Google
Network
Think
BGP
15
What Does a Mobile Network Look
Like?
Internet
Gatewa
y
• One point of access to
the internet: gateway
– All traffic must use the
same gateway
• Each carrier has many
mobile-networks
Canonical Mobile Network
Architecture
Courtesy: Q. Xu et al.
Location of Sprint’s Mobile
gateways
Seattle
Omaha
New York
Chicago
Washington
San Francisco
Phoenix
Kansas City
Los
Angeles
Atlanta
Dallas
Miami
12 or more gateways observed
30
Understanding the Structure of Mobile
Networks
• Requirements:
– Billing of different users
• Requires to be able to count all traffic
• Even when users move between towns
– Mobility
• Users will use different towers
• Must keep connections alive as user moves around
– Optimize user performance
• Change Video quality
• Change image quality
• Run a proxy
Understanding the Structure of Mobile
Networks
Internet
• Gateway (GGSN)
– A central point
– Runs advanced
proxies+transcoders
• Allows for:
– Billing
• Because it sees all
traffic
– Seamless mobility
• Runs a proxy
Implications of this Network
Background: DNS – How Load
Balancing Works
• Client Sends Request to
DNS-server
Server A
Server B
44.10/16
22.55/16
32.10/16
Server C
• Server uses client-IP
address to determine best
server
• For example
– Client-IP: 32.10.08.1
– DNS directs you to Server C
• For example
– Client-IP: 22.55.18.11
– DNS directs you to Server A
Background: DNS Load balancing with
Mobile networks
Gatewa
y
• Client Sends Request to
DNS-server
Server A
• Server uses client-IP address
to determine best server
Server B
44.10/16
22.55/16
• For example
32.10/16
Server C
– Client-IP: 32.10.08.1
– DNS directs you to Server C
– Indirect path
• Things get worse when
users drive around
–
32.10.08.1 can show up in different
locations!
Mobile IP Addresses are hard to
Geolocate
• Hard to figure out where a users is
– One Michigan’s cellular device’s IP is located to
places far away
Courtesy: Q. Xu et al.
Background BGP: How Internet Works
ISP A
ISP B
ISPC
Routing and network paths are limited to links exposed by BGP
• To send traffic to someone in the same city as you you may need to go to a
different state
Background BGP: How Internet Works
ISP A
ISP B
ISPC
Routing and network paths are limited to links exposed by BGP
• To send traffic to someone in your City, traffic may need to go to another city
Putting BGP and DNS Load-Balancing
together
Gateway
Mobile
Network
Public
Internet
Google
Server
Location
Google-Mobile
Peering point
• DNS gives you a server
– Based on your IP address
– So the server may be close to you
physically
• But your Mobile Network
Gateway may be far away from
the server
• Also the peering point to the
server’s ISP may be far away
from your gateway
6
GateWay
Mobile
Network
Public Internet
Google
Server
Location
Google-Mobile
Peering point
6
Types of Path Inflation
Four types of path inflation based on the
path segment where inflation occurs
Mobile
Network
Internet
Google
Network
● Mobile Network Inflation
● BGP Inflation
14
Mobile Network Inflation
Mobile Gateway is in a different City
But server is in your city
Local City
Mobile
Network
Remote City
Internet
Network
Google
Network
18
Case Study 1: Bad Gateway
Placement
AT&T New York
traffic enters public
Internet in Chicago
area
New
York
Chicago
1074km extra
distance
16ms extra latency
24
BGP Inflation
(Bad peering practices)
Peering point to Google’s ISP (server ISP) is
in a different city
Local City
Mobile
Network
Remote City
Google
Network
Internet
Network
17
Case Study 2: Lack of Peering
AT&T Seattle traffic
enters Google’s
network in Bay area
Seattle
1089km extra
distance
16ms extra latency
San
Francisc
o
25
• Cellular Networks
• Data Center Networks
• Current Class Grades
Mobile Traffic: Path Features
Mobile
Network
Internet
Google
Network
Think Data
center
15
What is a Data Center?
• Huge warehouse with racks of servers
– All cloud services run on a data center
• Challenges
– Power/Energy: cooling
– Performance: network throughput + latency
Canonical Data Center Architecture
Core
Aggregation
Edge Top-ofRack
Application
servers
How should the network be setup?
Which will provide best performance?
• Layer 2: Ethernet? ATM?
• Layer 3: Distance-vector? Link-state?
Layer 2: Ethernet Network
-Uses Flooding to know where a host is
-- uses a lot of bandwidth (doesn’t scale)
++ automatically learn addresses
++ enables mobility of a hosts
-Flat addressing  no aggregatioin:
--very large table (doesn’t scale)
-Each host comes with MAC-Address:.
++ No need to configure addresses
-Build a spanning tree
++ No loops in the Network
-- links unused
-- uneven loads
-- only uses one path
27
Layer 3: IP Networks
-Routing done though OSPF
+ Efficient use of links
+ No loops
- easy to reconfigure
-IP-addresses are hierarchical 
aggregation
- Must configure address for each host
- hosts can’t easily move hosts around
(must re-assign IP-address and netmask)
+Small forwarding tables (scales)
29
Comparison of L2 and L3
Architectures
Features
Ease of configuration
Optimality in addressing
Host mobility
Path efficiency
Load distribution
(Layer-2)
Ethernet
Bridging
(Layer 3)
IP
Routing










Data Centers Today
• Use Layer 3 for the performance benefits
• Enhance Layer 3 to allow for Mobility
– e.g. Microsoft’s VL2, VMWare’s NVP
– Each server has two IP addresses:
• Physical-Address: routing uses this address
• Logical-Address: servers identify each other using this address
– Adds a bit more complexity to the system
How does it work?
Src: Alice
Dst: Bob
Logical: Alice
Physical: H1
•
•
•
•
Logical: Bob
Physical: H2
Physical-Address: routing uses this address
Logical-Address: servers identify each other using this address
Alice wants to send to Bob: Alice uses Bob’s Logical-Address
The first device in the network rewrites all addresses from logicaladdresses to physical addresses.
How does it work?
Src: H1
Dst: H2
Logical: Alice
Physical: H1
•
•
•
•
Logical: Bob
Physical: H2
Physical-Address: routing uses this address
Logical-Address: servers identify each other using this address
Alice wants to send to Bob: Alice uses Bob’s Logical-Address
The first device in the network rewrites all addresses from logicaladdresses to physical addresses.
How does it work?
Src: H1
Dst: H2
Logical: Alice
Physical: H1
•
•
•
•
Logical: Bob
Physical: H2
Physical-Address: routing uses this address
Logical-Address: servers identify each other using this address
Alice wants to send to Bob: Alice uses Bob’s Logical-Address
The first device in the network rewrites all addresses from logicaladdresses to physical addresses.
How does it work?
Src: Alice
Dst: Bob
Logical: Alice
Physical: H1
•
•
•
•
Logical: Bob
Physical: H2
Physical-Address: routing uses this address
Logical-Address: servers identify each other using this address
Alice wants to send to Bob: Alice uses Bob’s Logical-Address
The first device in the network rewrites all addresses from logicaladdresses to physical addresses.
• Now you can move around: when you move your Physical address
changes but not your logical address
• Cellular Networks
• Data Center Networks
• Current Class Grades
Assignment 2 & 3
• Grades have been put up.
– If you have a ‘0’ on assignment 2 then your code
does not run with auto-graded
– Please send an email to see the TA
• Assign 3: avg 100/110, std: 24
• Assign 2: avg 70/100, std: 43
Current Class Grades
• Avg: 78
• Std: 14
• How to Calculate your grade:
Your grade = (Assign*50+ HW*10 + midterm *15)/75
Ignore extra-credit for now