Wide Area Networks II Flashcards
What is ATM?
Asynchronous Transfer Mode which is a data-link layer protocol.
Where is ATMs used?
Used in WAN Networks, to support the transfer of data with guarantees for quality of service. Used in the SONET/SDH backbone.
What does ATM provide?
-Integrated Voice, video and data
-High data rates
ATM is a form of?
Form of cell relay with large frames and packets which are segmented into cell-sizes (48-octet) pieces for transmission (5-octet headers).
53 Octets in total. Cells are switched across network. Reassembled at the destination. Unpredictable amounts of time between the arrival of these individual
“cells”
ATM Architecture?
ATM has layered arch.
AAL- ATM Adaption Layer.
Bitrate:
AAL1 - Voice ‘n’ Video (CBR)
AAL2 - Compressed Voice ‘n’ Video (VBR)
Unspecified Bitrate:
AAL34 - General User Data
AAL5 - TCP/IP
AAL5 frame
Channel number.
Header Error Check.
Type (control of data).
Cells loss priority (discardability)
refer to powerpoint.
ATM for Traffic Engineering or QoS
QoS can be configured at each ATM interface.
Constant Bit Rate
-Peak Cell Rate
- For max interval before being problematic
Variable Bit Rate (VBR)
- Sustainable Cell Rate (SCR)
- Can peak at certain level.
Uses of ATM for Traffic Engineering or QOS
Available Bit Rate (ABR)
- Minimum guaranteed rate is specified
Unspecified Bit Rate (UBR)
- Traffic is allocated to all remaining transmission capacity.
-Maximum Burst Length
-Guaranteed Minimal Bandwidth
ATM Link between Two Routers
picture on powerpoint.
Uses of ATM
Not used with desktop or “edge” parts of network.
- Not cost effective
Resides in high-speed core portion of network
- Supporting voice, compressed video and data.
Major feature of ATM is built in Quality of Service (QoS)
Advantages of ATM
Meets international and industry standards.
Works over most current high-speed WAN circuits.
Directly supports Quality of Service for multimedia transmission needs.
Cost competitive within core network.
Disadvantage of ATM
Complex operation and configuration (provisioing)
Somewhat inefficient due to (cell tax 10% overhead)
Not currently cost competitive at the “edges” of the network.
ATM designed to
Provide virtual circuit services across highly reliable media, with no error checks and retransmissions of data.
Optimize the connectionless generality of IP.
Transparent LAN Services (TLS)
Don’t have to deal with the WAN.
Don’t need to provision for frame relay, ATM, leased lines, etc.
With TLS, a carrier bridges between geographically separated LAN segments.
Making them all appear to be one big LAN.
Decreasing subscriber WAN management problems.
TLS are
TLS is ATM Circuits are a good example of heavy reliance on ATM by carriers.
Ethernet access to carriers ATM network,
called “Metro Ethernet” “Ethernet Transport” etc.
Available in all Ethernet Data Rates.
