X.25 Overview

1
X.25 Overview
2
An Introduction to X.25
X.25 Cloud
LAN Protocol
LAN Protocol
X.25
X.25
Virtual Circuit
IP AppleTalk Novell IPX Banyan VINES XNS
DECnet ISO-CLNS Apollo Compressed TCP
Bridging
3
X.25 Protocol Stack
OSI Reference Model
X.25 Protocol

Application
7

Presentation
6

Session
5

Transport
4
X.25
3
Network
3
Data Link
2
LAPB
2
Physical
1
Physical
1
4
X.25 (X.121) Addressing Format
4 decimal digits
Up to 10 or 11 decimal digits
Data Network ID Code
Network Terminal Number

• Addressing set by service provider

5
X.25 Encapsulation
IP Network
IP Network
X.25
Data-Link Frame (LAPB)
X.25 Header
IP Datagram

• Protocol datagrams are reliably carried inside
  X.25 frames

6
X.25 Virtual Circuits
Switched Virtual Circuits (SVCs)
Permanent Virtual Circuits (PVCs)

• Numbering for up to 4095 VCs per X.25 interface

7
X.25 Configuration Example
IP Address 10.60.8.2 X.121 Address 311082191234
IP Address 10.60.8.1 X.121 Address 311082194567
S1
S0
X.25
Cisco A
Cisco B
Cisco B
Cisco A
interface serial 1 encapsulation x25 x25 address
311082194567 ip address 10.60.8.1
255.255.248.0 x25 map ip 10.60.8.2 311082191234
broadcast
interface serial 0 encapsulation x25 x25 address
311082191234 ip address 10.60.8.2
255.255.248.0 x25 map ip 10.60.8.1 311082194567
broadcast
8
X.25 Local and XOT Switching
IP Internetwork
Local Switching
Remote Switching
9
Frame Relay Overview
10
Frame Relay Overview
DCE or FrameRelay Switch
DTE or CPE router
Frame Relay works here.

• Virtual circuits make connections
• Connection-oriented service

11
Frame Relay Terminology
LMI 500Active 400Active
DLCI500
Local Access LoopT1
Local Access Loop64 kbps
DLCI400
Local Access Loop64 kbps
12
Frame Relay Terminology (cont.)
Bc32 kbps
CIR64 kbps
T1
13
Selecting a Frame Relay Topology
Full Mesh
Partial Mesh
Star (Hub and Spoke)
14
Multipoint Subinterfaces Configuration Example
s2.110.17.0.2/24
RTR1
s2.210.17.0.1/24
s2.110.17.0.3/24
s2.110.17.0.4/24
15
Multipoint Subinterfaces Configuration Example
ltOutput Omittedgt ! interface Serial2 no ip
address encapsulation frame-relay ! interface
Serial2.2 multipoint ip address 10.17.0.1
255.255.255.0  bandwidth 64 frame-relay map ip
10.17.0.2 120 broadcast frame-relay map ip
10.17.0.3 130 broadcast frame-relay map ip
10.17.0.4 140 broadcast ! router rip network
10.0.0.0 ltOutput Omittedgt
16
Point-to-Point Subinterfaces Configuration Example
s2.1
10.17.0.0/24
RTR1
s2.2 s2.3 s2.4
10.18.0.0/24
s2.1
10.20.0.0/24
s2.1
17
Point-to-Point Subinterfaces Configuration Example
ltOutput Omittedgt interface Serial2 no ip
address encapsulation frame-relay ! interface
Serial2.2 point-to-point ip address 10.17.0.1
255.255.255.0 bandwidth 64 frame-relay
interface-dlci 110 ! interface Serial2.3
point-to-point ip address 10.18.0.1
255.255.255.0  bandwidth 64 frame-relay
interface-dlci 120 ! interface Serial2.4
point-to-point ip address 10.20.0.1
255.255.255.0  bandwidth 64 frame-relay
interface-dlci 130 ltoutput omittedgt
18
Common LAN Technologies
19
LAN Technology Overview
Ethernet Token Ring FDDI
FDDI Dual Ring
20
Ethernet and IEEE 802.3

• Several framing variations exist for this common
  LAN technology

21
Ethernet Frame Variations
22
Ethernet Frame Variations
AA
AA
CTRL
OUI
Ether Type
Upper Layer Data IP, AppleTalk
SNAP Frame
DSAP
SSAP
CTRL
DATA
802.2 Frame
Preamble
DA
SA
Length
802.2 Header and Data
FCS
802.3 Frame
23
High-Speed Ethernet Options

• 100BaseTX
• 1000BaseT/SX/LX/LH/ZX

24
Token Ring and IEEE 802.5
TokenRing

• IBMs Token Ring is equivalent to IEEE 802.5

25
Physical Layer Token Ring/802.5
Logical Topology
MSAU
Shielded or Unshielded Twisted-Pair

• Logically a ring, but physically a star
  configuration to MAU relays

26
The Token Ring/802.5 Interface
TokenRing
To0

• Cisco routers data link to Token Ring/802.5 uses
  interface named To plus a number (for example,
  To0)

27
Token Ring/802.5 Operation
T
A
T 0

• Token Ring LANs continuously pass a token

28
Token Ring/802.5 Operation
T
A
T 0
A
T 1
T
Data

• Token Ring LANs continuously pass a token or a
  Token Ring frame

29
Token Ring/802.5 Operation
T
A
A
T 0
T 0
T
A
T 1
T
Data

• Token Ring LANs continuously pass a token or a
  Token Ring frame

30
Token Ring/802.5 Media Control

• Fields in a frame determine priority and
  reservation for sharing media

31
FDDI
100 Mbps
FDDI Dual Ring

• Devices on FDDI maintain connectivity on dual
  counterrotating rings

32
FDDI Dual-Ring Reliability
When a failure domain occurs...
33
FDDI Dual-Ring Reliability
When a failure domain occurs...
34
FDDI Dual-Ring Reliability
When a failure domain occurs...
...wrap primary and secondary rings...
...wrap primary and secondary rings...
...maintaining network integrity
35
ATM
36
ATM Basics Review

• A compromise for voice, data, and video
• Hardware-based cell relay
• Larger frames are segmented and reassembled at
  ATM endpoints
• Can span both LAN and WAN
• Scales from a few Mbps to multi-Gbps
• QoS defined/negotiated when initial connection is
  made

Video
Voice
Data
ATM cells
ATM 53-octet cells are switched in hardware
37
ATM Cell Processing
38
Virtual Path and Virtual Channel
Virtual Channels (VCs)
ATM Physical LinkVirtual Channel Connection (VCC)
Virtual Path (VP)
e.g., OC-3, E3,OC-12
Virtual Path (VP)
Virtual Channels (VCs)
VCLogical Pathbetween ATM End points
Virtual Path(VP)Contains Multiple VCs
Virtual Channel Connection(VCC)Contains
Multiple VPs
Connection Identifier VPI/VCI
39
Well-Known VPI/VCIs
Terminating Connections
40
ATM Cell HeaderUNI Format
41
ATM Cell HeaderNNI Format
VPI
VCI
PT
CLP
HEC
12
16
3
1
8
32 Bits
8 Bits CRC
8 7 6 5 4 3 2 1
Bits Bytes
VPI
1 2 3 4 5
VPI
VCI
VCI
VCI
PT
CLP
HEC

• Larger VP field for trunking
• Distinction not very useful for private network

42
VP Switching/VP Cross-Connect
VCI 1 VCI 2
VCI 3 VCI 4
VPI 1
VPI 4
VCI 3 VCI 4
VCI 5 VCI 6
VPI 2
VPI 5
VCI 5 VCI 6
VCI 1 VCI 2
VPI 3
VPI 6
VP Switch

• Switching based on VPI only (central office
  trunk switching)

43
VP and VC Switching
VC Switch
VCI 2
VCI 3
VCI 4
VCI 1
VPI 3
VPI 2
VPI 1
VCI 4
VPI 2
VCI 1
VPI 1
VCI 2
VPI 3
VCI 3
VCI 1
VCI 1
VPI 5
VPI 4
VCI 2
VCI 2
VP Switch
44
ATM Switch Translation Table
Input
Output
4/55
VPI/VCI
Port
VPI/VCI
Port
2/39
1
4/55
2
6/64
2/39
4/55
2
2/39
1
6/64
1
2/89
3
2/89
3
6/64
1
2/39

• ATM switches translate VPI/VCI values
• VPI/VCI value unique only per interfacee.g.,
  locally significant and may be reused elsewhere
  in network

45
ATM Adaptation Layer
ServiceCategories
Bit Rate
ConnectionMode
TimingConcern
ApplicationExamples

• Bandwidth andthroughput guaranteed
• Good for voice and video

AAL1
CBR(Constant)
Connection-Oriented
Yes
ATM Adaptation Layer (AAL)

• Best effort bandwidth and throughput
• Good for live video,multimedia, LAN-to-LAN

AAL2
VBR (Variable)
Connection-Oriented
Yes
ATM Layer

• Best effort withcongestion feedback
• Reliable delivery of bursty traffic iflatency
  okay

AAL5
ABRUBR VBR (CBR)
Connection-Oriented
No
Physical Layer

• No guarantee
• For SMDS

AAL3/4
UBR(Un-specified)
Connection-less
No
46
AAL5
Payload Frame
Data Frame
ConvergenceSublayer (CS)
Convergence Sublayer PDU
AAL5
SAR PDU
SARSublayer
SAR PDU
SAR PDU
SAR PDU
ATM Cell
0x0
ATM Layer
ATM Cell
0x0
ATM Cell
0x0
0x1
ATM Cell

• CS trailer
• Length
• CRC-32
• Cell header
• Type empty, not EOM, EOM
• Payload 48 bytes
• Primary AAL for data

47
AAL5Frame and Cell Formats
AAL5 CPCS - PDU Frame n x 48 bytes
P A D
Payload Length
Control (CPI and UU)
User Data
CRC-32
4 bytes
2 bytes
0-65535 bytes
2byte
0-47 bytes
AAL5 CPCS PDU Trailer
SAR-PDU Payload 48 bytes
AAL5 SAR PDU 1 Cell Payload
CPI Common part indicator, current function
aligning the trailer to 8 bytes, currently
unused and set to 0 UU User-to-user indication,
currently unused and set to 0 PAD 0-47 bytes

• 53 5 (cell header) 48 (payload)

48
ATM Signaling,ATM Address Formats
49
Switched Virtual Channels (SVCs)
B-ICI
Public ATM Network
NNI
UNI
NNI
NNI
Private ATM Network

• SVC requires signaling
• ATM connection oriented
• ATM Forum UNI 3.x/4.0 signaling specification
• Based on ITU-T Q.2931

50
Signaling Concept
ATM Router A
Connect to B
OK
Connect to B
OK
Connect to B

• Signaling request
• Connection routedsetup path
• Connection accepted/rejected
• Data flowalong same path
• Connection teardown

Connect to B
OK
ATM Router B
51
ATM SVC Call Setup

• Call set up in software
• Cell switching in hardware
• Dynamic call establishment (call setup) with
  appropriate parameters (e.g., QoS CLR, CTD, CDV)

52
ATM SVC Call Release
Called Party
Calling Party
ATM Network
Release
Release
Release Complete
Release Complete
ES
ES

• Dynamic call teardown (call release) of virtual
  connection

53
Q.2931 Call Control
Mes Type
Mes Len
Call Ref
PD
Elements
Info

• Q.2931 call control message format at UNI

54
ATM Addressing Formats