Architecture of Network
Implementation
Reading: Chapters 3 and 4
Fall 2004
FSU CIS 5930 Internet Protocols
1
Layer-Based Communication
Models
End systems
Intermediate system
End systems
Anwendung
Application
Anwendung
Application
(N+1)-Protocols
Instance
(N+1)
Instance
(N+1)
Instance
(N+1)
Instance
(N+1)
(N)-protocol
Layer (N+1)
Layer (N)
Instance (N)
Instance (N)
(N)-protocol
Instance (N-1)
Instance (N-1)
Transmission medium
Fall 2004
Layer (N-1)
Transmission medium
FSU CIS 5930 Internet Protocols
2
Two Important Concepts in the
Layered Model
• Protocols
– Rules that two parties talk and understand each
other
– Horizontal
• Services
– Functions provided by a lower layer to the
neighboring upper layer
– Vertical
– Service interface (function calls)
Fall 2004
FSU CIS 5930 Internet Protocols
3
ISO/OSI Reference Model
ISO/OSI Reference model
Application
Presentation
Session
Transport
Network
Data link
Physical
Fall 2004
FSU CIS 5930 Internet Protocols
4
ISO/OSI Model
•
Physical layer
– Media types, coding methods, bit sequences vs. physical signals
•
Data link layer
– Moving data between two directly connected stations. Flow control, error
detection, etc. Shared medium: access control. LLC/MAC
•
Network layer
– Connectivity of networks. Packet routing/forwarding
•
Transport layer
– Concerning end-to-end functions between applications. Flow control, packet
ordering, etc.
•
Session layer
– Handling structured message exchange
•
Presentation layer
– Regulating data presentation (format)
•
Application layer
– Protocols for different applications, HTTP, SMTP, FTP, etc
Fall 2004
FSU CIS 5930 Internet Protocols
5
TCP/IP Reference Model
ISO/OSI reference model
Internet reference mode
7
Application
6
Application
(HTTP, SMTP, SSH)
Presentation
5
Session
4
Transport
Transport (TCP/UDP)
Network
Internet (IPv4/v6)
3
2
Data link
Data link
(802.x, PPP, SLIP)
1
Physical
Fall 2004
FSU CIS 5930 Internet Protocols
6
Interplay of Layers, Instances,
and Protocols
(N+1)-Layer
(N)-IDU
(N)-Layer
(N)-PCI
(N)-SDU
(N)-ICI
(N)-PDU
(N)-PCI
(N-1)-ICI
(N)-SDU
(N-1)-IDU
(N-1)-Layer
(N-1)-SDU
Fall 2004
(N-1)-ICI
FSU CIS 5930 Internet Protocols
7
PDU/PCI/SDU/ICI/IDU
• PDU: protocol data unit
– Elements exchanged between two protocol
instances
– PCI (protocol control information or packet
header) + SDU (service data unit)
• ICI: interface control information
– Passed from layer N to layer N-1 together with
layer N PDU
• IDU: interface data unit
– ICI + PDU
Fall 2004
FSU CIS 5930 Internet Protocols
8
Managing Network Packets in
Kernel
• Socket buffers
– Where packets are stored, manipulated.
• Socket buffer queues
– Linked list of socket buffers
Fall 2004
FSU CIS 5930 Internet Protocols
9
Socket Buffers (skb)
sk_buff_head
sk_buff
next
sk_buff
prev
list
stamp
net_device
dev
h
nh
mac
Packet data storage
dst
len
...
head
MAC-Header
IP-Header
UDP-Header
data
UDP-Data
tail
end
datarefp: 1
Fall 2004
FSU CIS 5930 Internet Protocols
10
Some important fields of skb
• prev, next, list
– Queue’s linked list
• sk
– Socket owning the packet
• dev
– Device receiving/sending packet
• h, nh, mac
– Pointers to the transport/network/MAC layer headers
• len
– Size of the packet
• data, head, tail, end
– Pointers associated with data packet field
• datarefp
– A counter indicating how many skb_buff points to the packet
– Not really a field of sbk_buff
Fall 2004
FSU CIS 5930 Internet Protocols
11
Updates of skb_buff as packet
passing different layers
sk_buff
sk_buff
sk_buff
next
next
next
prev
prev
prev
...
...
...
head
head
head
data
data
data
tail
tail
tail
end
end
end
Packet data storage
Packet data storage
Packet data storage
IP-Header
UDP-Data
datarefp: 1
Fall 2004
UDP-Header
UDP-Header
UDP-Data
UDP-Data
datarefp: 1
FSU CIS 5930 Internet Protocols
datarefp: 1
12
Operations on socket buffers
• Three types of operations
– Creating and releasing socket buffers
• alloc_skb(), dev_alloc_skb(), skb_clone(),
kfree_skb(), dev_kfree_skb()
– Manipulating fields of socket buffers
• skb_put(), skb_push(), skb_pull(),
skb_reserve()
– Managing socket buffer queues
• skb_queue_head(),etc
Fall 2004
FSU CIS 5930 Internet Protocols
13
Creating/releasing skb
• alloc_skb(size, gpf_mask)
• dev_alloc_skb(length)
• kfree_skb(skb)
• dev_kfree_skb(skb)
•skb_clone(skb,gpf_mask)
•skb_copy(skb,gpf_mask)
Fall 2004
FSU CIS 5930 Internet Protocols
14
Skb_clone()
skb_clone
sk_buff
sk_buff
sk_buff
next
next
next
prev
prev
prev
...
...
...
head
head
head
data
data
data
tail
tail
tail
end
end
end
Packet data storage
Packet data storage
IP-Header
IP-Header
UDP-Header
UDP-Header
UDP-Data
UDP-Data
datarefp: 1
Fall 2004
datarefp: 2
FSU CIS 5930 Internet Protocols
15
skb_copy()
skb_copy
sk_buff
sk_buff
sk_buff
next
next
next
prev
prev
prev
...
...
...
head
head
head
data
data
data
tail
tail
tail
end
end
end
Paketdatenbereich
Paketdatenbereich
Paketdatenbereich
IP-Header
IP-Header
IP-Header
UDP-Header
UDP-Header
UDP-Header
UDP-Data
UDP-Data
UDP-Data
datarefp: 1
Fall 2004
datarefp: 1
datarefp: 1
FSU CIS 5930 Internet Protocols
16
Manipulating skb fields
•
•
•
•
skb_put(skb,len)
skb_push(skb,len)
skb_pull(skb,len)
skb_reserve(skb,len)
After alloc_skb()
After skb_reserve()
An skb_buff containing data
After skb_put()
After skb_push()
Fall 2004
FSU CIS 5930 Internet Protocols
17
Socket buffer queue
sk_buff_head
next
prev
qlen: 3
sk_buff
sk_buff
sk_buff
next
next
next
prev
prev
prev
...
...
...
head
head
head
data
data
data
tail
tail
tail
end
end
end
Packet data
Packet data
Packet data
Fall 2004
FSU CIS 5930 Internet Protocols
18
Operations on socket buffer
queues
• Managing queue structures
– skb_queue_head_init(list)
– skb_queue_empty(list)
– skb_queue_len(list)
• Managing socket buffers in queues
– skb_queue_head(), skb_queue_tail(),etc
Fall 2004
FSU CIS 5930 Internet Protocols
19
Managing skb in queues
•
•
•
•
•
•
•
•
skb_queue_head(list, skb)
skb_queue_tail(list, skb)
skb_dequeue(list)
skb_dequeue_tail(list)
skb_insert(oldskb,newskb)
skb_append(oldskb,newskb)
skb_peek(list)
skb_peek_tail(list)
Fall 2004
FSU CIS 5930 Internet Protocols
20
Next time …
• Chapter 5: network devices
Fall 2004
FSU CIS 5930 Internet Protocols
21