Nokia 7705 SAR
The Nokia 7705 SAR (Service Aggregation Router) uses a specialized SAR ASIC with a unique fixed-segment buffer architecture designed for mobile backhaul and circuit emulation workloads.
| Field | Value |
|---|---|
| Total Buffer | ~200–300 MB per adapter card |
| Buffer Model | Fixed segments (non-shared) |
| Silicon | SAR ASIC (Nokia proprietary) |
| Buffer Unit | 512 bytes (chained) or 2304 bytes (unchained) |
| Target Role | Mobile backhaul, TDM adaptation, circuit emulation |
Buffer Architecture
Fixed Segment Mode — 2304-byte buffers
One packet occupies exactly one buffer segment. No chaining required. Simpler allocation, lower overhead.
Buffer Chaining Mode — 512-byte buffers
Packets are split across multiple linked buffer segments:
- First segment carries the packet header and partial payload
- Remaining payload is distributed across chained segments
This allows the router to handle fragmented or variable-length traffic efficiently.
QoS Interaction
- Each queue is configured with an MBS (Maximum Buffer Size) value
- Queues can be configured to claim more memory than physically available
- Buffer allocation is not guaranteed under congestion — the operator must size MBS values carefully relative to the physical memory on each adapter card
What It Handles Well
- TDM and mobile backhaul traffic with predictable, fixed packet sizes
- Circuit emulation (CES) workloads
- Deterministic per-flow buffer allocation
Limitations
- Less flexible than shared-memory systems — buffer exhaustion is possible under contention
- Fixed segment size creates overhead for very small or very large packets
- Not suitable for elastic packet buffering under variable congestion
See the Nokia Access/Aggregation architecture page for cross-platform comparison.